Curved ablation catheter

ABSTRACT

A curved ablation catheter imparts ablative energy to target tissue, for example, along a trabecular slope, e.g., in the right atrium along the isthmus between the ostium of the inferior vena cava and the tricuspid valve. The catheter is formed with a preset curvature that, when deployed, both translates linearly and increases in radius to aid in the formation of spot or continuous linear lesions. A method of treating atrial flutter employs the curved ablation catheter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application no.10/856,543, now U.S. Pat. No. 7,122,034, filed 27 May 2004 (the '034patent), now pending. The '034 patent is hereby incorporated byreference as though fully set forth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention is directed toward a curved ablation catheter forimparting ablative energy (e.g., radio frequency (RF) energy to targettissue, for example, along a trabecular slope e.g., in the right atriumalong the isthmus between the ostium of the inferior vena cava and thetricuspid valve. The catheter is formed with a preset curvature to aidin the formation of spot or continuous linear lesions.

b. Background Art

Catheters have been in use for medical procedures for many years.Catheters can be used for medical procedures to examine, diagnose, andtreat while positioned at a specific location within the body that isotherwise inaccessible without more invasive procedures. During theseprocedures a catheter is inserted into a vessel located near the surfaceof a human body and is guided to a specific location within the body forexamination, diagnosis and treatment. For example, one procedure oftenreferred to as “catheter ablation” utilizes a catheter to convey anelectrical stimulus to a selected location within the human body tocreate tissue necrosis. Another procedure oftentimes referred to as“mapping” utilizes a catheter with sensing electrodes to monitor variousforms of electrical activity in the human body.

In a normal heart, contraction and relaxation of the heart muscle(myocardium) takes place in an organized fashion as electrochemicalsignals pass sequentially through the myocardium from the sinoatrial(SA) node located in the right atrium to the atrial ventricular (AV)node and then along a well defined route which includes the His-Purkinjesystem into the left and right ventricles. Sometimes abnormal rhythmsoccur in the atrium which are referred to as atrial arrhythmia. Three ofthe most common arrhythmia are ectopic atrial tachycardia, atrialfibrillation, and atrial flutter. Arrhythmia can result in significantpatient discomfort and even death because of a number of associatedproblems, including the following: (1) an irregular heart rate, whichcauses a patient discomfort and anxiety; (2) loss of synchronousatrioventricular contractions which compromises cardiac hemodynamicsresulting in varying levels of congestive heart failure; and (3) stasisof blood flow, which increases the vulnerability to thromboembolism. Itis sometimes difficult to isolate a specific pathological cause for thearrhythmia although it is believed that the principal mechanism is oneor a multitude of stray circuits within the left and/or right atria.These circuits or stray electrical signals are believed to interferewith the normal electrochemical signals passing from the SA node to theAV node and into the ventricles. Efforts to alleviate these problems inthe past have included significant usage of various drugs. In somecircumstances drug therapy is ineffective and frequently is plagued withside effects such as dizziness, nausea, vision problems, and otherdifficulties.

An increasingly common medical procedure for the treatment of certaintypes of cardiac arrhythmia and atrial arrhythmia involves the ablationof tissue in the heart to cut off the path for stray or improperelectrical signals. Such procedures are performed many times with anablation catheter. Typically, the ablation catheter is inserted in anartery or vein in the leg, neck, or arm of the patient and threaded,sometimes with the aid of a guidewire or introducer, through the vesselsuntil a distal tip of the ablation catheter reaches the desired locationfor the ablation procedure in the heart. The ablation catheters commonlyused to perform these ablation procedures produce lesions andelectrically isolate or render the tissue non-contractile at particularpoints in the cardiac tissue by physical contact of the caidiac tissuewith an electrode of the ablation catheter and application of energy.The lesion partially or completely blocks the stray electrical signalsto lessen or eliminate arrhythmia.

One difficulty in obtaining in adequate ablation lesion usingconventional ablation catheters is the constant movement of the heart,especially when there is an erratic or irregular heart beat. Anotherdifficulty in obtaining an adequate ablation lesion is caused by theinability of conventional catheters to obtain and retain uniform contactwith the cardiac tissue across the entire length of the ablationelectrode surface. Without such continuous and uniform contact anyablation lesions formed may not be adequate.

It is well known that benefits may be gained by forming lesions intissue if the depth and location of the lesions being formed can becontrolled. In particular, it can be desirable to elevate tissuetemperature to around 50° C. until lesions are formed via coagulationnecrosis, which changes the electrical properties of the tissue. Forexample, when sufficiently deep lesions are formed at specific locationsin cardiac tissue via coagulation necrosis, undesirable ventriculartachycardias and atrial flutter may be lessened or eliminated.“Sufficiently deep” lesions means transmural lesions in some cardiacapplications.

One difficulty encountered with existing ablation catheters is assuranceof adequate tissue contact. Current techniques for creating continuouslinear lesions in endocardial applications include, for example,dragging a conventional catheter on the tissue, using an arrayelectrode, or using pre-formed electrodes. These catheter designs eitherrequire significant technical skill on the part of the surgeon inguiding and placing the catheter by sensitive steering mechanisms.Further, all of these devices comprise rigid eletrodes that do notalways conform to the tissue surface, especially when sharp gradientsand undulations are present, such as at the ostium of the pulmonary veinin the left atrium and the isthmus of the right atrium between theinferior vena cava and the tricuspid valve. Consequently, continuouslinear lesions are difficult to achieve. With a rigid catheter, it canbe quite difficult to maintain sufficient contact pressure until anadequate lesion has been formed. This problem is exacerbated oncontoured or trabecular surfaces. If the contact between the electrodeand the tissue cannot be properly maintained, a quality lesion isunlikely to be formed.

Thus, there remains a need for an ablation instrument that addressesthese issues with the existing designs and that permits the formation ofuniform spot and continuous linear lesions, including transmurallesions, on smooth or contoured surfaces, and that provides an ease ofuse not found in previous designs.

The information included in this background section of thespecification, including any references cited herein and any descriptionor discussion thereof, is included for technical reference purposes onlyand is not to be regarded subject matter by which the scope of theinvention is to be bound.

BRIEF SUMMARY OF THE INVENTION

The present invention is an ablation catheter that is relatively simpleto operate and that provides improved linear lesions. The catheter isparticularly advantageous for ablating a sloped surface of endocardialtissue. The catheter has an ablation means positioned on a distal end ofthe catheter, a proximal section, and a resilient curved section. Thecurved section is proximial and adjacent to the distal end and distaland adjacent to the proximal section. The curved section is adapted toconform to a constraint, for example, and introducer sheath, that altersthe curved section to assume a generally linear form, and to return to apreset curve when not otherwise constrained. When the catheter isgradually released from the constraint beginning at the distal end andprogressing proximally, the curved section of the catheter progressivelyfurls to form a hook-shape with an increasing radius of curvature togradually assured the preset curve. Further, the distal end of thecatheter translates linearly as it furls. The distal end also maintainsa generally constant orientation as the catheter furls and translatesand the ablation electrode thereby travels along a linear path.

In another embodiment, the invention is a device for ablatingendocardial tissue. The device is composed of two main components: asheath and a catheter. The sheath is provided for intravascularinsertion into a cardiac cavity. The sheath defines a lumen, an entranceport located at a proximal end of the sheath, and an exit port locatedat a distal end of the sheath. The catheter is provided for insertionwithin the lumen of the sheath. A distal tip of the catheter has anablation electrode and a distal portion of the catheter, proximal midadjacent to the distal tip, is adapted to resiliently retain a presetcurve when not otherwise constrained. The catheter is pliant whencompared to the sheath and, when residing with in the sheath, the distalportion of the catheter is constrained by the sheath. When the catheteremerges from the exit port of the sheath, the distal portion of thecatheter progressively furls to form a hook-shape with an increasingradius of curvature to gradually assume the preset curve. The cathetertranslates linearly as it furls and the distal tip maintains aninterface with and an orientation directed toward the trabecular surfaceas the catheter furls and translates wherein the ablation electrode isplaced in contact with the endocardial tissue along a linear path.

In another aspect of the invention, a method for ablating a trabecularsurface of endocardial tissue in a patient is discloses. The method isinitiated by introducing a sheath defusing a lumen and an exit portthrough a patient's vasculature into a cavity of the heart. The exitport of the sheath is then position within the heart cavity. A catheteris advanced through the lumen of the sheath to the exit port. Thecatheter is composed of a distal tip, an ablation electrode connectedwith the distal tip, a proximal section; and a resilient curved section.The curved section is proximal and adjacent to the distal tip and distaland adjacent to the proximal section. The curved section is also adaptedto conform to constraint by the sheath by assuming a generally linearform and to return to a preset curve when not otherwise constrained. Thecatheter is gradually deployed from the sheath to allow the resilientcurved section of the catheter to progressively furl into a hook-shapewith an increasing radius of curvature to gradually assume the presetcurve. The distal tip of the catheter is then oriented adjacent theendocardial tissue to be ablated and the ablation electrode is placed incontact with the endocardial tissue. The ablation electrode is energied.The distal tip is translated lineally as the curved section furls whilecontact is maintained between the ablation electrode and the endocaidialtissue and a lesion is thereby created in the endocardial tissue. Thesheath may further have all anchoring member, which is anchored to awall in the heart cavity.

In another embodiment of the invention, a method is provided fortreating atrial flutter in a patient. A sheath defining a lumen and anexit port is first introduced into the right atrium of the heart via theinferior vena cava. The exit port is positioned in the right atrium anda catheter is advanced through the lumen of the sheath to the exit port.The catheter is composed of an ablation electrode on a distal end, aproximal section, and a resilient curved section. The curved section isproximal and adjacent to the distal end and distal and adjacent to theproximal section. The curved section is further adapted to conform toconstraint by the sheath by assuming a generally linear form, and toreturn to a preset curve when not otherwise constrained. The distal endof the catheter is gradually deployed from the sheath to allow thecatheter to progressively furl into a hook-shape within the right atriumwith all increasing radius of curvature to gradually assume the presetcurve. The distal end of the catheter is oriented adjacent the isthmusbetween the inferior vena cava and the tricuspid valve. The ablationelectrode is then placed in contact with the endocardial tissue alongthe isthmus and is energized. The distal end of the catheter istranslated linearly as it furls while maintaining contact between theablation electrode and the endocardial tissue along the isthmus, therebycreating a linear lesion in the endocardial tissue along the isthmus.

Other features, details, utilities, and advantages of the presentinvention will be apparent from the following, more particular writtendescription of various embodiments of the invention as furtherillustrated in the accompanying drawings and defined in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an ablation catheter and sheath accordingto one embodiment of the present invention, showing the configuration ofthe catheter at several stages of translation.

FIG. 2 is an isometric view of the ablation catheter and sheath of FIG.1 detailing several component sections of the catheter.

FIG. 3 is an isometric schematic of the ablation catheter and sheath ofFIG. 1 depicted in situ in a right atrial cavity.

FIG. 4 is an isometric schematic of an alternate embodiment of theablation catheter of the present invention with a ball electrodedepicted in situ in the right atriuim cavity.

FIG. 5 is an isometric view of am alternative embodiment of the sheathwherein the ablation catheter emerges from the sheath via a side exitport.

FIGS. 6 and 7 are elevation views in cross-section of the embodiment ofthe ablation catheter and sheath of FIG. 5 in various stages of catheterdeployment wherein the catheter incorporates a wire to form a curvedsection.

FIG. 8 is a cross-section of the ablation catheter and sheath takenalong line 8-8 of FIG. 6.

FIGS. 9-11 depict a method of using the ablation catheter and sheath ofFIG. 8 to create a linear lesion in the right atrium.

FIG. 12 is an elevation view in cross-section of the ablation catheterof FIGS. 1 and 3 embodiment a brush electrode and revealing a primaryconductor making electrical contact with the filaments comprising thebrush electrode, and depicting a secondary lead (e.g., for athermocouple) extending adjacent to the primary conductor and becomingembedded within the brush filaments.

FIG. 13 is a cross-sectionial view of the ablation catheter taken alongline 13-13 of FIG. 12.

FIG. 14 is an enlarged view of the circled region of FIG. 12.

FIG. 15 is an isometric schematic of an alternate embodiment of theablation catheter of the present invention with a mesh electrodedepicted in situ in the right atrium.

FIG. 16 is an isometric schematic of an alternate embodiment of theablation catheter of the present invention with a virtual electrodedepicted in situ in the right atrium.

DETAILED DESCRIPTION OF THE INVENTION

Several embodiments of a curved ablation catheter 4 according to thepresent invention are depicted in the figures. As described furtherbelow, the curved ablation catheter 4 of the present invention providesa number of advantages, including, for example, mitigatingelectrode-tissue contact problems. The curved ablation catheter 4facilitates enhanced tissue contact in difficult environments (e.g.,during ablation of a contoured or trabecular surface on a beatingheart), whether creating a spot lesion or a continuous linear lesion, byfacilitating contact of an ablation electrode 8 with surface contours ofendocardial tissue. This is particularly useful for treatment of atrialflutter where it is desirable to create a linear lesion along thetrabecular slope of the isthmus between the ostium of the inferior venacava and the tricuspid valve in the right atrium.

FIG. 1 is an isometric view of one embodiment of an endocardial ablationdevice 2, including a catheter 4, a sheath 6, and an ablation electrode8. The sheath 6 defines a lumen 10 (depicted to better advantage inFIGS. 6-8), an entrance port located at a proximal end of the sheath(not shown), and an exit port 12 located at a distal end of the sheath6. (As used herein, “proximal” refers to a direction away from the bodyof a patient and toward the clinician. In contrast, “distal” as usedherein refers to a direction toward the body of a patient and away fromthe clinician.) The catheter 4 is designed for insertion within thelumen 10 of the sheath 6. Axiomatically, the diameter of the sheathlumen 10 is sized to accommodate the outer diameter of the catheter 4.The distal end of the catheter 4 is formed of a resilient material intoa preset curve or hook shape. An ablation electrode 8 is joined with adistal tip 18 of the catheter 4.

As indicated, the distal end of the catheter 4, between a proximalsection 14 and the distal tip 18, is formed into a curved section 16.The curved section 16 is resilient and maintains its preset hook-shapewhen not otherwise constrained. The curved section 16 may define an arcof between 90° and 270° or more. While the hook-shape of the curvedsection 16 is the normal orientation of the catheter 4, the catheter 4is pliant compared to the sheath 6 and, when introduced into the sheath6, the curved section 16 of the catheter 4 is constrained by the sheath6 and may conform to a more linear orientation of the sheath 6. Asdepicted in FIGS. 1 and 2, when the curved section 16 of the catheter 4is released from constraint by the sheath 4, the distal end of thecatheter 4 beginning at the distal tip 18, progressively furls to formthe hook-shape with an increasing radius of curvature to graduallyassume the preset curve inherent in the curved section 16. This is bestexemplified in FIG. 1, where as the catheter 4 progressively furls, theradius of curvature of the hook-shape at position A (shown in phantom)is r_(A). As the catheter 4 further furls, the radius of curvature ofthe curved section 16 of the catheter at position 13 (shown in phantom)is r_(B), which is a greater radius than r_(A). When the curved section16 is fully released from constraints indicated as position C on FIG. 1,the radius of curvature is r_(C), which is greater than r_(B). Inexemplary embodiments, the radius of curvature of the curved section 16may be between ½ cm and 3 cm. The are and radius of curvature of thecurved section 16 may be selected to allow the catheter to appropriately“fit” in various sizes of heart cavities, to position the catheter 4with respect to a particular tissue location for ablation application,or to orient the distal tip 18 and attached ablation electrode 8 at aparticular angle or direction.

In addition, as indicated in FIGS. 1 and 2, the distal tip 18 translateslinearly as the curved section 16 of the catheter 4 progressively furls.The ability of the catheter 4 to translate the distal tip 18 provides asignificant advantage in the ablative treatment of certain endocardialregions. For example, as shown in FIG. 3, the endocardial ablationdevice 2 of the present invention provides a simple mechanism to directan ablation electrode to treat a sloped trabecular surface 26 along theisthmus 24 between the inferior vena cava 22 and the tricuspid valve 28in the right atrium 20. The preset curve of the curved section 16maintains the orientation of the ablation electrode 8 toward thetrabecular slope 26. Further, as the catheter 4 is deployed from theexit port 12 of the sheath 6, the radius of curvature of the hook-shapeof the curved section 16 increases and the distal tip 18 translateslinearly, allowing the ablation catheter 8 to contact any portion of thetrabecular slope 26 desired. This is achievable by merely introducingthe catheter 4 into the right atrium 20 through the sheath 6 and withoutextensive training by the surgeon as required in the manipulation of asteerable catheter or other similar device. Additional benefits,applications, and results are described further below.

As depicted in FIG. 2, the catheter wall 44 may be formed from sectionsof different materials. For example, the catheter wall 44 may becomposed of Pebax® resins (AUTOFINA Chemicals Inc. Philadelphia Pa.), orother polyether-block co-polyamide polymers, wherein different formulasare used to create the desired material stiffness within each section ofthe catheter 4. These sections of different material enable the catheter16 to have, for example, different mechanical properties (e.g.,flexibility) at different locations along the catheter shaft. Forexample, the proximal section 14 of the catheter wall 44 may be formedof a relatively stiffer material than the curved section 16, allowingfor greater transfer of control exerted at the proximal end of thecatheter 4 to the distal end. The curved section 16 may be made of arelatively more pliant material than the proximal section 14 tofacilitate the formation of the hook-shape of the curved section 16, aswell as provide a level of suspension to the distal tip 18 as furtherdescribed below. The distal tip 18 may be of greater stiffness than thecurved section 16 as well to provide appropriate support to the ablationelectrode 8. The distal tip 18 may further be composed of a radiopaquemarker to allow a clinician to visualize the position of the tip of thecatheter 4 in the heart. In one embodiment, for example, for use inablating within the right atrium as described in further detail herein,the length of the curved section 16 may be approximately 4 cm and thelength of the distal tip 18 may be approximately 1 cm. The catheter wall44 may or may not comprise these sections of different materialdepending upon the intended application for the catheter 4. Although thecatheter 4 depicted in FIG. 1 (and as shown in cross-section in FIG. 13)has a circular cross section, the cross-section of the catheter wall 44may be other than circular.

The preset curve of the curved section 16 may be formed, for example, byincorporating a wire 60 with some degree of shape memory within thecatheter 4 as shown in FIGS. 5-8. The wire 60 is oriented longitudinallyalong the length of the catheter 4 and may run the entire length of thecatheter 60, extend only through the curved section 16 to the distal tip18, or it may run for some intermediate length. The wire 60 may beencapsulated within the catheter wall 44 as depicted in FIG. 8, it mayreside within the catheter lumen 30, or the catheter 4 may define asecondary lumen (not shown) in which the wire 60 resides. The wire 60may be flat (as shown) to resist twisting torque that might transfer tothe curved section 16 and impact the alignment.

The wire 60 may be composed of stainless steel or other material withthe ability to deform and then return to a preset shape. In oneembodiment, the wire 60 may be a material with a shape-memory, forexample, NiTinol, a nickel-titianium (NiTi) alloy. Shape-memory metals,such as NiTinol are materials that have been plastically deformed to adesired shape before use. Then upon heat application, either from thebody as the catheter is inserted into the vasculature or from externalsources, the fixation element is caused to assume its original shapebefore being plastically deformed. NiTinol and other shape-memory alloysare able to undergo a “martensitic” phase transformation that enablesthem to switch from a “temporary” shape to a “parent” shape attemperatures above a transition temperature. Below that temperature, thealloy can be bent into various shapes. Holding a sample in position in aparticular parent shape while heating it to a high temperature programsthe alloy to remember the parent shape. Upon cooling, the alloy adoptsits temporary shape but when heated again above the transitiontemperature the alloy automatically reverts to its parent shape.Alternately, or in addition, shape-memory materials may also be superelastic—able to sustain a large deformation at a constanttemperature—and when the deforming force is released they return totheir original undeformed shape.

Common formulas of NiTinol have transformation temperatures rangingbetween −100 and +110° C., have great shape-memory strain, are thermallystable, and have excellent corrosion resistance, which make NiTinolexemplary for use in medical devices for insertion into a patient. Forexample, a catheter may be designed with a NiTinol wire with atransition temperature around or below room temperature. Before use thecatheter is stored in a low-temperature state. By flushing the catheterwith chilled saline solution the NiTinol wire can be kept in itsdeformed state while positioning the catheter for deployment at thedesire site. When deployed from the sheath, the flow of chilled salinesolution can be stopped and the catheter warmed by body heat, or warmsaline can be substituted to allow the wire to recover its“preprogrammed” shape.

In another embodiment, the catheter itself may be composed of a shapememory material, for example, certain polymers (e.g., as available frommnemoScience GmbH, Aachen, Germany). Certain monomeric components, forexamnple, oligo (e-caprolactone) dimethacrylate and n-butyl acrylate,when combined generate a family of polymers that display excellentshape-memory properties. Such polymers can be programmed into shape inseconds at about 70° C. and can withstand deformations of severalhundred percent. In this exemplary embodiments the oligo(e-caprolactone) dimethacrylate furnishes the crystallizable “switching”segment that determines both the temporary and permanent shape of thepolymer. By varying the amount of the comonomer, n-butyl acrylate, inthe polymer network, the cross-link density can be adjusted. In thisway, the mechanical strength and transition temperature of the polymerscan be tailored over a wide range.

In another embodiment of the inventions the sheath 6 is formed with allanchoring member 58 at its distal end as shown in FIGS. 5-11 and 1-16.The anchoring member 58 defines a side port 62, which operates as theexit port in this embodiment. A distal finger 64 of the anchoring member58 extends distally beyond the opening for the side port 62. The distalfinger 64 may be pressed or anchored against tissue in a cavity of theheart, for example, an atrium wall 56 as shown in FIGS. 9-11, to helpstabilize the endocardial ablation device 2 while the heart is beating.The anchoring member 58 may be composed of a stiffer material thanportions of the sheath 6 proximal to the anchoring member 58 tofacilitate stability of the anchoring member 58 to act as a platform fordeployment of the catheter 4 from the side port 62. Increased stiffnessof the anchoring member 58 also helps provide increased structuralintegrity of the sheath 6 around the side port 62 opening, as such alinear slot in the sheath 6 weakens the wall of the sheath 6. Theanchoring member 58 may be composed of a polymer of greater hardnessand/or stiffness than the proximal portion of the sheath 6 or it mayeven be composed of stainless steel or another suitable material toprovide the desired rigidity and structral integrity.

As depicted in FIGS. 5-7, the catheter 4 begins to furl immediately upondeployment from the sheath 6 in the region of the side port 12. When thesheath 6 is positioned as desired in the heart, for example, in theright atrium as in FIG. 9 with the anchoring member set securely againstthe atrial wall 56, the catheter 6 is positioned on the isthmus 24adjacent the inferior vena cava 22 with the ablation electrode 8 incontact with the tissue 52. As the catheter 4 is further deployed fromthe sheath 6, the curved section 16 continues to furl and alsotranslates linearly in the direction of the anchoring member 58 asindicated by comparison of the positions of the catheter 4 in each ofFIGS. 9-11. The deployment of the catheter 4 maintains the distal tip 18and the attached ablation electrode 8 in contact with the trabecularslope 26 of the isthmus 24.

The creation of a linear lesion 54 in the tissue 52 of the isthmus 24 ofthe right atrium 20 is depicted schematically in FIGS. 9-11. In thisprocedure, a linear series of ablation lesions is created from theannulus of the tricuspid valve 28 to the inferior vena cava 22 in theisthmus 24 of right atrial tissue 52 bordering the Eustachian ridge.This isthmus 24 of tissue is critical to the large right atrialreentrant circuit responsible for atrial flutter. The ablation lesions54 damage atrial tissue 52 preventing the conduction of electricalimpulses through the critical isthmus 24. When the line of conductionblock is complete, the atrial flutter circuit is shorted and thearrhythmia is cured.

As shown in FIG. 9, a linear lesion 54 is initiated by the deployment ofthe catheter 4 from the side port 62 of the sheath 6. The catheter 4immediately furls as a portion of the curved section 16 emerges from thesheath 6. The furling of the curved section 16 orients the distal tip 18toward the sloped isthmus 24 and the ablation electrode 8 is placed incontact with the tissue 52. Upon activation of a source of ablativeenergy connected with the ablation electrode 8, the tissue 52 isnecrotized and a lesion 54 is formed. As the catheter 4 is furtherdeployed, the distal tip 18 maintains an orientation directed toward thetrabecular surface 36 of the isthmus 24 as the catheter furls andtranslates. The ablation electrode 8 likewise maintains an interfacewith the endocardial tissue 52 on the isthmus 24 along a linear path asshown in FIGS. 10-11 to create a continuous linear lesion 54.

In the particular embodiment of FIGS. 9-11, a brush electrode 8 isdepicted as the ablation electrode 8. A continuous linear lesion 54 (asshown in FIG. 11) is able to be formed because of the superior abilityof the filaments 40 of the brush electrode to maintain contact with thetissue 52 and to transfer ablative energy to the tissue 52. In analternative embodiment, for example as shown in FIG. 4, the catheter 4may incorporate a ball electrode 8′ as the ablation electrode. Althoughnot as capable of conforming to trabecular surfaces as the brushelectrode 8, the ball electrode 8′ may be desired for use in certaincircumstances for creating spot ablations.

The novel brush electrode 8 of the type depicted in FIGS. 1-3 and 5-14was originally disclosed in U.S. patent application Ser. No. 10/808,919filed 24 Mar. 2004, entitled Brush Electrode and Method for Ablation,which is hereby incorporated by reference in its entirety as thoughfully set forth herein. As shown in greater detail in FIGS. 12-14 thebrush electrode 8 may be composed of a plurality of filaments 40, eitherconductive or nonconductive, arranged in a bundle mid protruding fromthe distal tip 18 of the catheter 4. Such a flexible brush electrode 8provides enhanced tissue contact particularly for use on contoured ortrabecular surfaces.

The filaments 40 may be constructed from a variety of differentmaterials including noncondcutive materials semi-conductive materials,and conductive materials. For example, the filaments 40 may be formedfrom metal fibers, metal plated fibers, carbon compound fibers, andother materials. Very thin, carbon fibers may be used. Relativelythicker but less conductive Thunderon® acrylic fibers (Nihon SanmoDyeing Company Ltd., Kyoto, Japan) may also be used for the brushelectrode filaments 40. Nylon fibers coated with conductive material mayalso be used. Filaments 40 constructed from metal plated fibers, likecoated nylon fibers, may comprise flattened areas around their outersurfaces, resulting in the filaments 40 having noncircularcross-sectional shapes. The brush filaments 40 may be insulated fromeach other, or they may be in electrical contact with each other.Conductive or nonconductive fluids may flow interstitially between andamong the filaments 40 themselves or along the outer surface of thefilaments 40.

An embedded portion 48 of the filaments 40 forming the brush electrode 8may be contained within the catheter lumen 30 at the distal tip 18 ofthe catheter 4 while an exposed portion 46 may extend distally from thedistal tip 18. The exposed portion 46 of the brush electrode 8 mayproject a few millimeters from the distal tip 18 of the catheter 4. Thedistance that the exposed portion 46 of the brush electrode 8 extendsfrom the distal tip 18 of the catheter 18 varies depending upon a numberof factors including the composition of the filaments 40 comprising thebrush electrode 8 and the particular area to be treated with the brushelectrode 8. The distal tip 18 of the catheter 4 may itself beconductive or nonconductive.

FIG. 12 is a cross-sectional view of the catheter 4 of FIG. 1, forexample, in a linear orientation. A primary conductor 32 having aninsulated portion 34 and an uninsulated portion 36 carries ablativeenergy (e.g., radio frequency, current) from an energy source in acontroller to the brush electrode 8. The primary conductor 32 extendswithin the catheter lumen 30 along a longitudinal axis of the catheter4. The primary conductor 32 may comprise, for example, insulated copperwire with an uninsulated portion 36 in electrical contact with the brushelectrode 8. In this embodiment, the uninsulated portion 36 of theprimary conductor 32 is formed or tied in a loop or noose 38 around theembedded portion 48 of the filaments 40 of the brush electrode 8, asshown to better advantage in FIGS. 13-14. At the loop or noose 38,ablative energy is transferred from the primary conductor 32 to theconductive filaments 40 of the brush electrode 8. In this embodiment,the uninsulated portion 36 of the primary conductor 32 is connected tothe embedded portion 48 of the brush electrode 8 so that the connectionbetween the primary conductor 32 and the brush electrode 8 is protectedwithin the catheter wall 44. A secondary lead 42, also shown in FIGS.12-14, may extend substantially parallel to the primary conductor 32. Adistal end of the secondary lead 42 is embedded with the filaments 40comprising the brush electrode 8. The secondary lead 60, when present,may be operatively connected to a sensor embedded in the brush electrode8 (e.g., a thermal sensor, an ultrasound sensor, or a pressure sensor).

FIG. 14 is an enlarged view of the circled region of FIG. 12. As shownin FIG. 14, the brush electrode 8 may have a relatively flat workingsurface 50 at the distal end 32 of the brush electrode 8. In otherwords, in this depicted embodiment, all of the filaments 40 comprisingthe brush electrode 8 extend approximately the same distance from thedistal tip 18 of the catheter 4. Thus, the brush tip provides arelatively flat working surface 50 comprising the longitudinal ends ofthe filaments 40. The catheter wall 44 at the distal tip 18 of thecatheter 4 provides mechanical support for the filaments 40 and may alsoprovide electrical shielding.

The filaments 40 may alternatively be trimmed to provide a variety ofconfigurations and shapes for the working surface 50 of the brushelectrode 8, which may provide advantages for special applications ofthe brush electrode 8. For example, a blade-shape may be formed bycreating an edge of longer filaments of the brush electrode resulting ina line of contact with the tissue. Alternatively, the brush electrode 8may have a wedge-shaped working surface 50 to facilitate angularplacement and increase the area of the working surface 50. Thisconfiguration may be advantageous for point applications of ablativeenergy. As another example, the working surface 50 of the brushelectrode 8 may have a concave portion or channel, which may bebeneficial for wrap-around applications and provide advantages whenablating curved surfaces like the outer surface of a blood vessel.Alternatively, the working surface 50 of the brush electrode 8 may havea convex, trough-shaped tip, which may be beneficial, for example, whenreaching into troughs or depressions on a contoured surface. The workingsurface 50 of the brush electrode 8 could also be domed, hemispherical,a frustum, or conical, coming nearly to a point at the most distal endof the brush electrode 8, with its longest filaments 40 proximal to thelongitudinal axis of the catheter 4. The brush electrode 8 is depictedin many of the drawings with a circular cross section, but it may havedifferent cross-sectional configurations.

In one embodiment, conductive or nonconductive fluid may flow though thecatheter lumen 30 from a fluid source (e.g., a pump and reservoir in acontroller) to the brush electrode 8. When the fluid flows through thebrush electrode 8 it creates a wetbrush electrode in which impingingjets of fluid traveling interstitially impact the tissue 52 at aninterface between the tissue 52 and the brush electrode 8 to helpcontrol temperature changes at the interface. When using conductivefluid and either conductive or nonconductive filamnents 40, the brushelectrode 8 may act as a virtual electrode. If there is no directcontact between conductive filaments and the tissue 52, or the filaments40 are entirely nonconductive, the conductive fluid flowing through thecatheter lumen 30 makes the electrical contact at the interface betweenthe brush electrode 8 and the tissue 52.

The brush electrode 8 according to the present invention deliversablative energy to the tissue via the conductive filaments 40 alone, viathe conductive fluid alone, or via both the conductive filaments 40 andthe conductive fluid. In the latter two configurations, the brushelectrode 8 is referred to as a wet-brush electrode. Since it ispossible for the conductive fluid to escape from the exposed portion ofthe wet-brush electrode prior to reaching the working surface 50 at thedistal tip of the wet-brush electrode, there is some ablative energyleakage to the surrounding blood. The leakage of ablative energy to thesurrounding blood is in part due to direct contact between the blood andthe conductive filaments and in part due to the conductive fluidescaping between the filaments 40 to the surrounding blood, particularlywhen substantial splaying of the filaments 40 occurs.

Alternatively, the ablation electrode may embody other electrode formsto achieve particular desired results. For example, FIG. 15 depicts allembodiment of the present invention in which a mesh electrode 8″ isintegrated with the catheter wall 44 along a portion of the curvedsection of the catheter 4 and approaching the distal tip 18. A meshelectrode 8″ of this exemplary type is disclosed more full in U.S.patent application Ser. No. 10/645,892, filed 20 Aug. 2003, and entitledAlbation Catheter and Electrode, the disclosure of which is herebyincorporated by references as though fully set forth herein. In thisembodiment, the arc of travel of the curved section of the catheter 4 isgreater than in other embodiments, for example, that of FIG. 1. Thisallows the linearly designed mesh electrode 8″ in the catheter wall 44to more fully lie against the tissue 52 on the isthmus 24 to create alinear lesion 54. Another embodiment of the present invention mayincorporate a virtual electrode 8′″ as depicted in FIG. 16. A virtualelectrode 8′″ supplies conductive fluid that is then energized withablative energy to for a lesion in the tissue 52. A virtual electrode8′″ of this exemplary type is disclosed more full in U.S. patentapplication Ser. No. 10/608,297, filed 27 Jun. 2003, and entitledAblation Catheter Having a Virtual Electrode Comprising Portholes and aPorous Conductor, the disclosure of which is hereby incorporated byreferences as though fully set forth herein. Again, the are of travel ofthe curved section of the catheter 4 is greater than in otherembodiments, for example, that of FIG. 1. This allows the linearlydesigned virtual electrode 8′″ with its ports iin the catheter wall 44to apply fluid to the tissue 52 to create a linear lesion 54.

Although various embodiments of this invention have been described abovewith a certain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit or scope of this invention. It is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative only of particularembodiments and not limiting. All directional references (e.g.,proximal, distal, upper, lower, upward, downward, left, right, lateral,front back, top, bottom, above, below, vertical, horizontal, clockwise,and counterclockwise) are only used for identification purposes to aidthe reader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Connection references (e.g. attached, coupled, connected, andjoined) are to be construed broadly and mas include intermediate membersbetween a collection of elements and relative movement between elementsunless otherwise indicated. As such, connection references do notnecessarily infer that two elements are directly connected and in fixedrelation to each other. It is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted as illustrative only and not limiting. Changes in detail orstructure may be made without departing from the basic elements of theinvention as defined in the following claims.

What is claimed is:
 1. A device for interfacing an electrode with anendocardial tissue, the device comprising a sheath for intravascularinsertion into a cardiac cavity, the sheath comprising a lumen; anentrance port located at a proximal sheath portion; an exit port locatedat a distal sheath portion; and a catheter for insertion through theentrance port into the lumen of the sheath, the catheter comprising adistal catheter portion, wherein the distal catheter portion iselastically straightenable for insertion within the sheath, and whereinthe distal catheter portion returns to a preset, resilient curve whenunconstrained by the sheath; an electrode on the distal catheterportion; a distal catheter tip distal to the distal catheter portion;wherein when the distal catheter tip exits through the exit port, thepreset, resilient curve of the distal catheter portion increases inradius of curvature and directs the orientation of the distal cathetertip towards the endocardial tissue and maintains an interface with theendocardial tissue, translating the electrode along the endocardialtissue along a substantially linear path.
 2. The device of claim 1,wherein the endocardial tissue is trabecular tissue.
 3. The device ofclaim 1, wherein the exit port comprises a slot on the side of thedistal sheath portion.
 4. The device of claim 3, wherein the distal endof the sheath extends beyond the slot to form an anchoring member. 5.The device of claim 1, wherein the preset, resilient curve comprises anarcuate shape.
 6. The device of claim 5, wherein the arcuate shapecomprises a hook shape.
 7. The device of claim 6, wherein the hook shapecomprises a radius of curvature between 0.5 cm and 3 cm.
 8. The deviceof claim 1, wherein the distal catheter portion comprises a shape memorywire.
 9. The device of claim 1, wherein the preset, resilient curveorients the distal tip of the catheter at an angle between 90° and 270°from the direction of orientation of the exit port at the distal end ofthe sheath.
 10. The device of claim 1, wherein the electrode comprises abrush electrode.
 11. The device of claim 1, wherein the electrodecomprises a sensing electrode.
 12. The device of claim 11, wherein theelectrode further comprises an ablation electrode.
 13. A device forinterfacing an electrode with an endocardial tissue, the devicecomprising a sheath for intravascular insertion into a cardiac cavity,the sheath comprising a lumen; an entrance port located at a proximalsheath portion; an exit port located at a distal sheath portion; ananchoring member adapted to anchor the distal sheath portion in theendocardium; and a catheter for insertion through the entrance port intothe lumen of the sheath, the catheter comprising a distal catheterportion, wherein the distal catheter portion is straightenable forinsertion within the sheath, and wherein the distal catheter portionadopts a preset, resilient curve upon exiting the sheath; an electrodeon the distal catheter portion; a distal catheter tip distal to thedistal catheter portion; wherein when the distal catheter tip exitsthrough the exit port, the preset, resilient curve of the distalcatheter portion progressively increases in radius of curvature anddirects the orientation of the distal catheter tip towards theendocardial tissue and maintains an interface with the endocardialtissue, coupling the electrode with the endocardial tissue along asubstantially linear path.
 14. The device of claim 13, wherein theanchoring member comprises a distal finger extending distally beyond theexit port.
 15. The device of claim 14, wherein the anchoring member isstiffer than a portion of the sheath proximal to the anchoring member.16. The device of claim 13, wherein the endocardial tissue is trabeculartissue.
 17. The device of claim 13, wherein the exit port comprises aslot on the side of the sheath.
 18. The device of claim 13, wherein thepreset, resilient curve comprises an arcuate hook shape.
 19. The deviceof claim 13, wherein the electrode comprises a brush electrode.
 20. Amethod for ablating a trabecular surface of endocardial tissue in apatient, the method comprising introducing a sheath defining a lumen andan exit port through a patient's vasculature into a cavity of the heart;positioning the exit port within the heart cavity; advancing a catheterthrough the lumen of the sheath to the exit port, wherein the cathetercomprises, a distal tip; an ablation electrode connected with the distaltip; a proximal section; and a distal catheter portion proximal to thedistal tip, wherein the distal catheter portion is elasticallystraightenable for insertion within the sheath, and wherein the distalcatheter portion returns to a preset, resilient curve when unconstrainedby the sheath; gradually deploying the catheter from the sheath to allowthe preset, resilient curved section of the catheter to progressivelyfurl into a hook-shape with a decreasing radius of curvature togradually assume the preset curve; orienting the distal tip of thecatheter adjacent the endocardial tissue to be ablated; contacting theablation electrode with the endocardial tissue; energizing the ablationelectrode; translating the distal tip of the catheter linearly as thepreset, resilient curved section of the distal catheter portion furlswhile maintaining contact between the ablation electrode and theendocardial tissue; and creating a lesion in the endocardial tissue. 21.The method of claim 20, further comprising the step of anchoring ananchoring member of the sheath to a wall in the heart cavity.
 22. Amethod for treating atrial flutter in a patient comprising introducing asheath defining a lumen and an exit port into the right atrium of theheart via the inferior vena cava; positioning the exit port in the rightatrium; advancing a catheter through the lumen of the sheath to the exitport, wherein the catheter comprises an ablation electrode on a distalend; a proximal section; and a preset resilient curved section, proximaland adjacent to the distal end and distal and adjacent to the proximalsection, with sufficient flexibility to conform to constraint by thesheath by assuming a generally linear form, and to return to a presetcurve when not otherwise constrained; gradually deploying the distal endof the catheter from the sheath to allow the catheter to progressivelyfurl into a hook-shape within the right atrium with a decreasing radiusof curvature to gradually assume the preset resilient curve; orientingthe distal end of the catheter adjacent the isthmus between the inferiorvena cava and the tricuspid valve; contacting the ablation electrodewith the endocardial tissue along the isthmus; energizing the ablationelectrode; translating the distal end of the catheter linearly as itfurls while maintaining contact between the ablation electrode and theendocardial tissue along the isthmus; and creating a linear lesion inthe endocardial tissue along the isthmus.
 23. The method of claim 22,further comprising the step of anchoring an anchoring member of thesheath to a wall of the right atrium adjacent the tricuspid valve.